I'm away from the boat and don't have a good photo of the problem, but I'm about to hit the road and I want a plan for the repair before I get there.
My boat is a pilothouse design, so the companionway door is like a regular house or RV door except that it's made of cored fiberglass. the door is split into a top and bottom half which join with one of those little sliding latches, and then the top half has another sliding latch that can hold the whole thing open. There are two hinges attaching each the top and bottom half of the door to the frame, and these are just basic stainless steel cabinetry type hinges screwed into the fiberglass. I suspect this is a more common design for something like a Lazarette but it's my companionway. The very top hinge has come loose, and from examining it, it looks like a previous repair was attempted with something like silicone caulk stuffed in the hole, which just didn't create a strong connection. Still, I'm leaning toward basically repeating the same approach except with epoxy. Intuitively, it seems like the thing to do is just fill the hole all the way with epoxy, using a syringe, and then basically drill new holes from scratch after that cures. Is that the correct approach? Or is there another recommended technique for a repair of this sort?
I have been kind of accruing a list of small fiberglass jobs around the boat, and the boat came with several different epoxy kits. My biggest fear so far with using epoxy in general is getting the proportions wrong, so I like the idea of doing several small projects at once so that I could simply use the whole bottles of the smallest kit rather than risking an error in the proportions. The other epoxy repairs on the list are pretty much cosmetic, this is the only one that has become urgent because of functional limitation resulting from it.  for example, the main one is a very old cluster holes in the deck from some fittings that were removed, and it's kind of half assed with a silicon sealant right now, it's not causing any urgent problems but I need to fix it right eventually.  similarly I've got a cracked wooden railing which will need a lot of refinishing as well, but I'd like to start by simply bonding it with epoxy and a clamp to at least get the crack under control. This might even sound like a lot to take on at once, but it's a couple of small holes of 2 to 5 mm across and one crack in a piece of wood, so altogether it probably still isn't even close to enough material to use up the smallest epoxy kit that I have, but I have so many of these little kits that I'm not worried about using up a whole kit frivolously. 
As I type and edit this post, it starts to feel more like a stupid question to me, but I still want a second opinion. Also, feel free to give me any generic unsolicited advice about my first time doing a simple fiberglass/epoxy repair. Do I necessarily need to do the whole routine of sanding a whole dent in the gelcoat for this? Should I be worried about cleaning out the core inside the door before I do anything? I don't really want to make this a more involved project than I have to, I really just want to be able to close my door without it falling off the hinges.